Furnace pressure regulation



J. J. KLINKER I 2,225,871

FURNACE PRESSURE REGULATION Dec. 24, .1940.

Filed Nov. 10, 1958 "Hill JOHN J. ft" L INKER 15 in the furnace walls.

Patented Dec. 24, 1940 UNITED STATES.

FURNACE PRESSURE REGULATION John J. Klinker, Decatur, 111., aasignor toA. W. Cash Company, Decatur, lll., a corporation of Delaware ApplicationNovember 10, 1938, Serial No. 239,897

8 Claims. (Cl. 236 -14) This invention relates to furnace pressure regulation, and more particularly to the regulation of pressure in a furnacehaving a forced draft air supply which is started automatically inresponse to a demand for heat.

It is common practice to utilize an automatic regulator to control thepressure in a combustion chamber or furnace by actuation of a suitablylocated damper. Ordinarily, however, such a regulator cannot move thedamperwith suiiicient rapidity to prevent a substantial increase in thefurnace pressure when the forced draft air supply is started, and as aresult flame and smoke issue into the room from all cracks and openingsThis problem has been recognized, and one solution heretofore proposedincludes means to initiate operation of the regulator in response to ademand for heat, and to delay the starting of the forced draft airsupply for a predetermined time thereafter. Such a system has thedisadvantage that it may require readjustment whenever the availablestack draft changes, and such variations in draft may be caused byweather changes, by varying the numher of furnaces discharging into acommon stack,

or otherwise. A different solution heretofore proposed includes means toinitiate operation of the regulator in response to a demand for heat,and to delay the starting of the forced draft air supply until thedamper has reached a predetermined position. This system likewise hasthe disadvantage that it may require frequent readjustment, since thereis no certainty that a particular damper position will ensure sufficientfurnace draft to prevent a flare back when the fan or other forced draftdevice is placed in operation.

It is accordingly one object of the invention to provide an improvedautomatic control system for a forced draft furnace whereby flare backsmay be avoided.

It is a further object of the invention to provide simple and reliablemeans to ensure an adequate draft in a furnace when the forced draft airsupply is started, regardless of changes in the draft available at thefurnace outlet.

It is a further object of the invention to provide simple and reliablemeans to delay the starting of the forced draft air supply in responseto a demand for heat, until a predetermined draft is obtained in thecombustion chamber.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of par sset forth in the specification and covered by the 55 claims appendedhereto.

Referring to the drawing illustrating one embodiment of the invention,and in which like reference numerals indicate like parts.

The single figure is a diagrammatic elevation,

partly in section, of a, forced draft furnace having automatic means forregulating the pressure therein.

The embodiment illustrated comprises walls l0 forming a furnacecombustion chamber H fired. by means of an underfeed stoker l2 having are- 5 tort I 4 and tuyere blocks l5. Air is supplied to the space l8beneath the retort by means of a forced draft fan l8 driven by a motorI9. The motor illustrated is an electric motor directly connected to thefan, and it also serves to actuate 10 the stoker l 2 through achain-and-sprocket drive 20. The heat from the furnace II is utilized togenerate steam in a boiler 22 mounted thereabove. The furnace gases flowin contact with the boiler heating surfaces and then escape 16 through agas outlet or uptake 23 to a suitable stack (not shown). The pressure inthe combustion chamber I l is controlled by a suitably located damper 24having an operating arm 25. In the illustrated embodiment this damper islocated 20 in the gas outlet 23.

The damper 24 is controlled automatically by a suitable regulatorresponsive to variations in the pressure in the furnace ll. Forthispurpose I preferably utilize an automatic regulator 21 of 25 the typedisclosed in the'patent to Temple No. 1,992,048 granted February 19,1935. This regu lator comprises a pilot valve mechanism 28 .suppliedwith a suitable fluid under pressure through a pipe 29 and connected bytubes 3| to a hy- 30 draulic motor 32. This motor 32 is connected to thedamper operating arm 25 by means of a rod 33. The regulator 21 isconnected to the furnace II by means of a pipe 34, so that the furnacepressure is effective to actuate the regulator. 35 The regulator isadjusted to maintain a furnace pressure slightly below atmosphericpressure, say

a negative pressure of one-tenth inch water column.

The electric motor I! is connected to a suitable 40 electrical supply 36by means of conductors 31 which lead throughan electro-magneticall tated switch or contactor 38. This switch is provided with a holding coil39, and the parts are so arranged that upon energization of this co l 45the switch will be closed and the motor l9 will start.

In order to control the rate of steam generation automatically, means isprovided for starting and' stopping the motor I! at intervals inaccordance with the demand for steam. For this purpose I have shown apressure-actuated master switch 4! of the well-known mercury tube typeconnected by a pipe 42 to the steam delivery pipe 43 of the boiler 22,and arranged to close at a predetermined minimum steam pressure and toopen at a predetermined maximum steam pressure. This switch 4| serves tocontrol the supply of electricity from a suitable source 45 to a pair ofpower leads 46 and 41. The source 45 is shown as independent of thesource 36, but it will be understood that this is not necessarily thecase.

It will now be apparent that if the holding coil 39 is connecteddirectly across the power leads 46 and 41, as has been customary in thepast, certain difficulties will arise. With the fan l8 shut down,combustion will be very slow, and

the regulator 21 will hold the damper 24 in a" nearly closed position tomaintain the desired pressure in the furnace II. If now the "steampressure drops sufficiently to close the switch 4|, and the fan motor 19is immediately started, the regulator will be unable to open the damperfast enough to prevent a considerable increase. in the furnace pressure,with attendant emission of flame and smoke.

In order to overcome this difficulty I provide means to unbalance theregulator 21 immediately upon closure of the pressure-actuated switch4|, so that the regulator will immediately begin to increase the draftin the combustion chamber by opening the damper 24, and I provide meansto close the switch 38 and start the motor i! only after the furnacedraft has been increased to a predetermined value. The unbalancing of thregulator is preferably effected by venting it to atmosphere, and forthis purpose a valve 49 is mounted in the pipe 34 to provide anatmospheric vent 50 controlled by a valve member 5|. The valve membernormally rests by gravity in a position to close the vent. The valvemember 5| is directly connected to the plunger 53 of a solenoid 54, theparts being so arranged that upon energization of the solenoid,theplunger and valve member will be raised and the vent 50 opened. It isalso desirable to close communication with the furnace ll upon openingof the vent 50, so as to avoid a rush of air through the vent and intothe furnace. For this purpose I provide a partition wall 55 whichextends across the interior of the valve 49 between the vent and thefurnace. This wall is provided with a port 56 located directly above thevent 50 and in a position to be closed by the valve member if when thelatter is raised by energization of the solenoid 54. It will be seenthat this construction provides means whereby the regulator 21 may beconnected to the furnace II when it is desired to control the furnacepressure, and to the atmosphere when it is desired to open the damper 24and obtain a high draft in the furnace while the forced draft air supplyis started.

Means is provided to energize the solenoid 54 immediately upon closureof the master switch 4| and to maintain energization thereof until apredetermined draft has been attained in the combustion chamber ll,whereupon the motor I9 is started and the solenoid 54 de-energized. Inthe preferred embodiment illustrated I provide a regulator 58 comprisinga pressure-responsive device in the form of a horizontal flexiblediaphragm 59 which divides the interior of the regulator into upper andlower chambers 60 and 6| respectively. The upper chamber 60 is vented toatmosphere through an opening 63, while the lower chamber BI issubjected to the draft in the furnace combustion chamber ll through apipe 64. This pipe may lead to the furnace directly, or (as illustrated)it may be connected to the pipe 34 at a point between the valve 49 andthe furnace. The central portion of the diaphragm 59 rests upon apressure plate 65 therebeneath which is supported by an up-' wardlyextending coiled tension spring 66. The upper end of the spring 88 isconnected to a apparent from the above disclosure.

nut 68 mounted upon a vertical screw 69. This screw can be rotatedmanually to adjust the tension of the spring. Upward movement of thediaphragm under the influence of the spring is limited by lugs 10 withinthe chamber 60. Beneath the lower chamber 6| there is provided a switch12 of the well-known mercury tube type having an upwardly extendingoperating rod or pin 13. This rod 13 is urged upwardly into contact withthe pressure plate 65 by means of a light coiled compression spring 14surrounding the upper portion of the rod within the lower chamber 6|.The switch "is supported from the'wall' of the chamber Si by means of atube or pipe 15 through which the rod 13 extends with a comparativelyclose sliding lit to prevent entrance of air into the chamber. Thesevarious parts are so constructed and arranged that the diaphragm 59 isnormally held upwardly against the lugs 10 by means of the spring 66,and the switch 12 is open. If however the draft or suction in thefurnace chamber I l reaches a predetermined value, so that apredetermined difference exists between the atmospheric pressure on theupper side of the diaphragm and the furnace pressure on the lower sideof the diaphragm, the diaphragm will be drawn downwardly in op positionto the force of the spring 66, and the switch I2 will be closed. 7

Such closure of the switch 12, in response to the attainment of apredetermined furnace draft, is utilized to effect de-energization ofthe solenoid 54 and energization of the holding coil 39. For thispurpose there is provided an electromagnetically actuated switch orcontactor 11 having a holding coil 18, this switch being constructedwith one normally closed contact 19 and two normally open contacts andill. The normally closed contact 19 is connected in series with thesolenoid 54 across the power leads 56 and 41, and the holding coil 78 isconnected in series with the switch 12 across the said power leads. Thenormally open contact 80 is connected across the switch 12 to serve as ashunt therefor. The normally open contact 8| is connected in series withthe holding coil 39 of the switch 38 across two of the leads from thepower supply 36.

The operation of the invention will now be Assuming that suflicientsteam pressure exists in the boiler 22 to maintain the master switch iiopen, the fan and stoker will be shut down and the various parts will beas shown in the drawing, with the regulator 21 controlling the damper 24to maintain a normal predetermined draft in the furnace II. If now thesteam pressure drops sufiiciently to close the switch 4|, this willenergize the solenoid 54 through the closed contact 19 and raise thevalve member 5i, opening the vent 50 and closing the port 56. This willsupply atmospheric pressure through the vent 50 to the regulator 21,which is adjusted to maintain a normal furnace pressure slightly belowatmospheric. The regulator will therefore be unbalanced, and the damper24 will start to open, increasing the draft in the furnace. When thisdraft reaches the comparatively high predetermined value for which thespring 66 of the regulator 58 has been adjusted, the diaphragm 59 ofthis regulator will move downwardly, closing the switch 12. This willenergize the holding coil 18 of the switch 11, the contact 19 will open,and the contacts 80 and ill will close. Closure of the contact 8| willenergize the holding coil 39 tact 19 will de-energize the solenoid 54,and the plunger 53 with the valve member 5i will drop, opening the port56 and closing the vent 50. This will connect the regulator 21 to thecombustion chamber II, and the regulator will then control the damper 24in accordance with the combustion chamber pressure, maintaining thispressure at a predetermned value slightly below atmospheric pressure.Closure of the contact 80 will shunt the switch 12. Hence, when thediaphragm 59 is moved upwardly by the spring 66 upon restoration ofnormal combustion chamber pressure, and the switch 12 is consequentlyopened, the holding coil 18 will nevertheless remain energized. The fanand stoker will continue to operate until the steam pressure hasincreased sufficiently to open the master switch 4|. This willde-energize the holding coil 18, closing contact 19, and openingcontacts 80 and 8|. This will de-energize the holding coil 39, and theswitch 38 will open, stopping the motor IS. The various parts will thenbe in their original positions.

It will now be clear that the fan and stoke cannot start until theswitch 12 is closed, and

, this can take place only when a predetermined draft has beenestablished in the combustion chamber. as determined by the adjustmentof the spring 66 of the regulator 58. This is true regardless ofvariations in the available stack draft produced by changes in weatherconditions, changes in the number of boilers in service, or otherwise.Hence the invention is far more practical and fool-proof thanarrangements heretofore proposed.

Having thus described my invention. what'I claim as new and desire tosecure by Letters Patent is:

1. A control system for a furnace having a forced draft air supplycomprising means to start and stop the air supply in response to changesin,

the demand for heat, and means responsive to the furnace draft andarranged to establish a comparatively high predetermined draft in thefurnace temporarily immediately prior to. each starting of the airsupply.

2. A control system for a furnace having a in the demand for heat. meansto maintain a.

comparatively low normal draft in the furnace, and means responsive tothe furnacedraft and arranged to increase the furnace draft temporarilyto a predetermined value immediately prior to each starting of the airsupply.

3. A control system for a furnace having a forced draft air supplycomprising means to start and stop the air supply in response to changesin the demand for heat, a regulator responsive to the furnace draft andarranged to maintain. said draft normally at a comparatively low value,and

means responsive to the furnace draft and arranged to unbalance theregulator and increase the furnace draft temporarily to a predeterminedvalue immediately prior to each startingof the air supply 4. A controlsystem for a furnace having a forced draft air supply comprising aregulator responsive to the furnace draft and arranged to maintain saiddraft normally at a comparatively low value, means to unbalance theregulator and increase the furnace draft in response to a demand forheat, and-control means responsive to the furnace draft and arranged tostart the air supply and restore the regulator to balance when the drafthas increased to a predetermined value.

5. A control system for a furnace having a forced draft air supplycomprising a regulator responsive tothe furnace draft and arranged tomaintain said draft normally at a value slightly below atmosphericpressure, means providing a normally closed atmospheric vent for theregulator, means to open the vent and thus increase the furnace draft inresponse to a demand for heat, and control means responsive to thefurnace draft and arranged to start the air supply and close the ventwhen the draft has increased to a predetermined value. i

6. A control system for a furnace having a forced draft air supplycomprising a regulator.

responsive to the furnace draft and arranged to maintain said draftnormally at a comparatively low value, a solenoid arranged whenenergized to unbalance the regulator and increase the furnace draft,means to energize the solenoid in response to a demand for heat, andcontrol means responsive to the furnace draft and arranged to start theair supply and de-energize the solenoid when the. draft has increased toa predetermined the solenoid in response to a demand for heat.

and a control switch responsive to the furnace draft and arranged tostart the air supply and deenergize the solenoid when the draft hasincreased to a predetermined value.

8. A control system for a furnace having a forced draft air supplycomprising a regulator responsive to the furnace draft and arranged tomaintain said draft normally at a comparatively low value, a solenoidarranged when energized to unbalance the regulator and increase thefurnace draft, two electrical power leads, a master switch to energizethe power leads in response to a demand for heat, an electricalcontactor having a holding coil and three contacts one of which isnormally closed and two of which are normally open, a control switchconnected in series with the holding coil across the power leads,-

means responsive to the furnace draft and arranged to close the controlswitch when the furnace draft has increased to a predetermined value,means connecting the normally closed con- JOHN J. KLI'NKERI

